Powered underwater motive devices have been known since the 1950's. Most of those earlier devices were metal and were built like small submarines. Access was had through hatches which had to be securely bolted or clamped in order to resist taking on water at depth. Water is harmful to both motors and batteries and must be sealed out. As a result, the underwater motive devices were large, bulky and designed with a mind to limit outside access to limit the sealing areas provided for service access.
Recent improvements in underwater motive devices have related to the safety of operation, including a slight delay in starting to prevent inadvertent operation. In addition, sealed chambers have been introduced to keep water out of the battery and motor compartments.
However, for small motive devices, providing an integral housing complete with sealing of the battery and motor compartment has proved difficult for users to easily access the battery and motor compartment. The only alternative to a strong seal was unacceptable as a weaker seal would cause the taking of the device to depth to result in cyclical pressure leakage. Where the device is used in salt water, even the slightest leakage can be disastrous.
Seals achieve their integrity by resilient sealing force and area. Both force and area contribute to the necessity for high force of replacement and removal. In a prior underwater motive device, air pressure and a pump were utilized to provide internal assist pressure to unseal the battery and motive compartments. Battery exchange required some setup and interconnectivity time.
In another underwater motive device, a cam system is used to provide significant sealing and un-sealing force. In underwater motive devices which are more oblong, the placement of battery, actuaction switch, sealing member, motor and the like can be arranged in a more orderly fashion. Further, where an underwater motive device is of a larger variety, it is expected that a larger more specialized battery will be supplied and which will have a longer residence time. Further, longer, more powerful devices will achieve greater depth for longer periods of time and the ability to seal out high pressure is paramount.
Where a power supply, typically a battery is to be used, the design of underwater motive devices can generally allow sealing to be accomplished most effectively during manufacturing, but not around the battery. Batteries for such service should be sealed to the extent possible but most are not made for pressurized submersion for any period of time. Any water leakage and especially salt water leakage can ruin a battery. Where an underwater motive device has a larger power supply a larger and more expensive battery is at risk. Further, as the assembly of the underwater motive device is large, larger seals and more complex battery and battery connection arrangements have to be made. For smaller underwater motive devices, there are significant problems associated with the placement of the handles, operating switch, motor and accommodating battery change out.
Another problem for underwater motive devices is the sophistication and time required in battery changeout. For professional divers, a larger more expensive unit which is capable of longer operation is required. Because commercial divers are paid a high hourly contract rate, the equipment used will be dictated by minimizing battery changeout and maintenance time. Underwater motive devices have generally not been available to more economically minded swimmers and skin divers.
Any more simplistic underwater motive device should be more available based upon both cost and operability. To expand the useage of the underwater motive device, younger and weaker users should be able to operate a much more inexpensive device. The aspects to be overcome are cost, ability to access the battery department and the ability to operate from batteries which are less specialized and more common, as well as lowering the sophistication of the individuals who can maintain and operate the underwater motive device.